This invention relates to apparatus and methods of thermally processing substrates.
In most thermal processing methods and apparatus substrate temperatures are precisely measured and controlled over a wide range of temperatures. For example, Peuse et al. (U.S. Pat. No. 5,660,472) describes a rapid thermal processing (RTP) system that includes a plurality of pyrometers configured to measure substrate temperature based upon the radiation emitted from a substrate which is being heated by an array of broad-band radiation sources. At temperatures above 300-325.degree. C., the substrate temperature may be controlled within a desired range by a feedback controller which adjusts the radiation source power based upon signals received from one or more of the pyrometers. At temperatures below about 300-325.degree. C., however, the emission intensity from the substrate within the wavelength range to which the pyrometers are sensitive generally is insufficient for the pyrometers to accurately measure substrate temperature. Contact probes (e.g., thermocouples) may be used to monitor substrate temperatures at lower temperatures. Such direct temperature measurement techniques, however, are difficult to reliably implement because of problems associated with degradation of the contact probe and maintenance of a stable thermal contact between the probe and the substrate.
In general, substrates are thermally processed in a series of one or more phases. For example, some thermal processes include a pre-heating phase during which the substrate is heated to an initial temperature before the substrate is loaded completely into the processing chamber and processed with a prescribed heating cycle.